The invention relates to a combination instrument for a motor vehicle, the instrument having a front frame and a printed circuit board arranged behind the front frame, and having display instruments and warning lights which are provided for displaying information on a display panel, are attached to the printed circuit board and are in electrical contact with the latter. Light shafts are arranged between the warning lights and the display panel, and the front frame has cutouts for the display instruments and for holding a viewing window which is arranged in front of the display panel.
Such combination instruments are used in large numbers in modern motor vehicles and are therefore known. In these instruments a central housing contains the light shafts and ensures that the printed circuit board is at a specific distance from the front frame, the central housing being arranged between the front frame and the printed circuit board. The light shafts prevent the warning lights from emitting light onto adjoining areas of the display panel and are covered by, for example, colored, transparent plastic disks.
A drawback of the known combination instrument is that the central housing represents an additional component to be produced and fitted. As a result, the combination instrument is very cost-intensive. Furthermore, the central housing requires a relatively large amount of space, leading to a considerable structural depth of the combination instrument.
The invention is based on the problem of designing a combination instrument of the type mentioned at the outset in such a manner that it is as simple as possible to fit and as inexpensive as possible to produce, and has a particularly low structural depth.
According to the invention, this problem is solved by means of a combination instrument for a motor vehicle, the instrument having a front frame and a printed circuit board arranged behind the front frame, and having display instruments and warning lights which are provided for displaying information on a display panel. The display instruments and the warning lights are attached to the printed circuit board and are in electrical contact with the latter. Light shafts are arranged between the warning lights and the display panel, and the front frame has cutouts for the display instruments and for holding a viewing window which is arranged in front of the display panel. In accordance with a feature of the invention the front frame is produced integrally with the light shafts and the display panel is formed by a transparent diaphragm screen which is attached to the front frame and has cutouts for the display area of the display instruments, and the printed circuit board bears against the light shafts and/or against spacers of the front frame.
This configuration means that, in the combination instrument according to the invention, there is no need for a central housing to be fitted separately between the printed circuit board and the front frame, with the result that the instrument has a particularly low structural depth. The display panel, apart from the area of the display instruments, is covered with a diaphragm screen for the warning lights, so that there is no longer any need for individual plastic disks for covering the light shafts. Since the combination instrument according to the invention has particularly few components, it is very simple and therefore inexpensive to produce and fit. An observer is unable to see the front frame in the region of the diaphragm screen and the display instruments, so that the front frame can be configured in many different ways. By way of example, the front frame may be configured in the form of a trough or, in order to increase its stability, may be of honeycomb structure. In the fitted position of the combination instrument, the diaphragm screen covers any edges of the front frame. The display instruments and warning lights which are in electrical contact with the printed circuit board may, for example, be attached directly to the printed circuit board. Spacers for the printed circuit board are required only at those positions of the front frame at which there are no light shafts.
According to an advantageous refinement of the invention, the diaphragm screen can be attached to the front frame particularly easily if it is adhesively bonded to the front frame.
The diaphragm screen is particularly thin and, according to another advantageous refinement of the invention, can be produced inexpensively if it is formed of a film.
According to another advantageous refinement of the invention, the warning lights can be used to graphically display particularly diverse information on the display panel while using the same or similar warning lights if the diaphragm screen is printed with symbols, markings, lettering and/or colored panels which represent information.
The information which can be represented on the display panel by the warning lights can be seen only when the warning lights are actuated if the diaphragm screen has a dark hue and the symbols, markings, lettering and/or colored panels are printed on their side facing toward the front frame and/or on their side facing away from the front frame. The result is a so-called black panel effect.
Incandescent bulbs which emit white light are particularly suitable as warning lights. The use of identical warning lights further reduces the costs of the combination instrument.
It has proven particularly advantageous if light sources which emit colored light are used for the warning lights. Colored LEDs, for example, are suitable for this purpose. If colored light sources are used, there is no need for colored printing of the associated display panels on the diaphragm screen, a fact which is extremely successful in saving costs.
To improve the light efficiency of the warning lights, the light shafts could have a reflective coating on their inner sides. However, according to another advantageous refinement of the invention, such a coating can be avoided if the front frame is made from a light-reflecting material.
It is highly advantageous to use, for example white, plastic as the material for the front frame.
According to another advantageous refinement of the invention, the front frame can be produced particularly inexpensively from plastic, using the injection molding process, if it is made from polypropylene.
The adhesive bond between the front frame, which is made from plastic, and the diaphragm screen is particularly reliable, according to another advantageous refinement of the invention, if the front frame is provided, at least in the region of the diaphragm screen, with a layer of paint. In this case, this layer of paint serves as an adhesion promoter between the adhesive and the plastic of the front frame.
According to another advantageous refinement of the invention, the layer of paint increases the contrast of the display panel if it is colored, e.g. black.
According to another advantageous refinement of the invention, a slight inaccuracy of alignment of the diaphragm screen on the front frame does not lead to overlapping of the cutouts for the display instruments through the diaphragm screen if the cutouts for the display instruments in the front frame and the diaphragm screen are delimited by a diaphragm-screen ring.
The diaphragm-screen ring could, for example, be formed integrally with the diaphragm screen and engage around the cutouts in the front frame. This design of the diaphragm-screen ring does facilitate fitting the diaphragm screen on the front frame and also increases the outlay on producing the diaphragm screen. The diaphragm-screen ring increases the manufacturing outlay on the combination instrument according to the invention only to an insignificant extent if the diaphragm-screen ring is produced integrally with the front frame.
According to another advantageous refinement of the invention, the diaphragm-screen ring can be fitted particularly easily to the front frame by clipping the ring into the front frame.
According to another advantageous refinement of the invention, the diaphragm-screen ring additionally increases the stability of the front frame if it is adhesively bonded into the front frame.
According to an advantageous refinement of the invention, the diaphragm-screen ring is automatically centered in the cutout of the front frame during assembly if it is made from a hot-formable or cold-formable material, and is secured in the front frame by plastic deformation.
Inaccuracies in the cutouts in the front frame and the diaphragm screen are invisible to an observer of the display panel if, according to another advantageous refinement of the invention, the diaphragm-screen ring has an encircling edge which engages over that area of the diaphragm screen which adjoins the cutouts. This makes it possible to make the cutouts in the diaphragm screen larger than in the front frame, so that precise alignment of the diaphragm screen with respect to the front frame is no longer required.
According to another advantageous refinement of the invention, the display instruments are visually emphasized if the diaphragm-screen ring is made from metal.
The diaphragm-screen ring has a low weight and is particularly inexpensive if, according to another advantageous refinement of the invention, the ring is made from plastic and has a metal-coated or painted surface. However, the ring may also, in a particularly simple variant, be made solely from plastic.
It is of considerable economic benefit if the diaphragm-screen rings of the individual display instruments are designed as a unit, for example wherein the rings are connected via webs.
The display instruments in the combination instrument according to the invention could, for example, be illuminated from the side of the observer. However, incident illumination of this nature often leads to undesirable reflections. According to an advantageous refinement of the invention, the display instruments of the combination instrument can be illuminated without risk of reflections if an optical conductor plate, which is provided with light sources or adjoins light guides, is arranged behind a transilluminatable dial which is fitted in the front frame.
The combination instrument according to the invention allows a wide variety of possible optical configurations if the wall of the front frame has a variable wall thickness. This configuration of the front frame allows, by way of example, individual display instruments to be set back or emphasized.
It is often necessary to display additional information in the combination instrument. According to another advantageous refinement of the invention, this is achieved, in a simple manner, by the fact that the dial and/or the front frame has a cutout for a flat screen, e.g. an LCD display. Such a flat screen allows numerous warning indications to be displayed in text form.
The printed circuit board could, for example, be screwed or clipped to the front frame. However, since the combination instrument often has a rear wall, according to another advantageous refinement of the invention a separate attachment of the printed circuit board to the front frame can be avoided if the printed circuit board and the dial are clamped between the front frame and the rear wall.
For the purposes of assembly without using tools, the combination instrument according to the invention can be fitted together readily if the front frame is connected to the rear wall by means of a clip-in connection. This allows substantially automated assembly of the combination instrument.